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Safety gap experiment
Ed Sonderman visited me last week while in the Northeast, so I gave him a
show and tell about my coil, and showed him the remains of my recently
failed rolled capacitor. Ed related a similar experience he had, where
he had blown some commercial caps on his RSG/pig-powered coil. The cap
vendor advised him to put safety gaps across his cap, and Ed was
surprised to find that, due to mains-resonance, could not stop his safety
gaps from firing, until he killed the resonance with an inductive ballast.
He suggested that I put a safety gap across my cap, so I threw together a
simple gap consisting of two 3/4" dia loops of solid #14 copper wire. I
was appauled to see it arcing continuously with a seperation of 0.75"!
My main single-segment static gap is only 0.34", how could this be so
much greater?
Suspecting that it may be due to differing radii of curvature between the
two gaps, I fashioned a new cap safety gap, this time using a pair of
stainless steel tablespoons, back to back. Now, the safety only fires
below a seperation of 0.375", and then, only after about 10 seconds of TC
operation. Then I connected the same spoon gap in parallel with my main
gap and observed the same result. I suspect that the difference now
between the .375" and the .34" gaps is due to air flow through the main
gap and not the other.
The lesson here is that safety gap construction must use large-radius
electrodes. Curved wire electrodes generate too much corona and break
down the gap prematurely. The same principals no doubt applies to main
gap design.
Gary Lau
Waltham, MA USA